To me, shared hosting and load balancing are mutually exclusive.
For any sizeable web application, you want exclusive, REALLY dedicated hosting.
Virtualisation sucks incredibly badly for database servers because it does not share out IO bandwidth well between VMs. You want dedicated hardware.
If there is the slightest chance you can afford it, buy dedicated hardware. You'll get waay better IO performance, and most importantly, YOUR application won't be dependent on what IO is happening in other peoples' VMs.
Performance and shared hosting are mutually exclusive.
Mark